1991 Vette surging/misfire loss of power (Full Version)

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1991 Vette surging/misfire loss of power

  

myfirstone -> 1991 Vette surging/misfire loss of power (7/1/2008 8:01:58 AM)

I am new to this forum and just wanted to thank everyone in advance for any help they may be able to provide.  After many years of wanting a Corvette, I''ve finally purchased a 1991 L98 model with 72K. This car has sat the last couple years and been run sparingly in that time. Upon test driving and driving 50 miles home after purchasing it ran pretty well other than a slight hesitation in which case i figured it would need tuned up anyway.  However after getting it home it has started to sputter and hesitate and lose as much power as it can without stalling when accelerating. It makes a popping sound that almost sounds like it is backfiring through the intake. This condition does not occur when idling or revving in park even after it warms up. I have changed the MAP and Coolant temp sensors after getting advice from another C4 owner and the problem still exists. The fuel pressure is 35lb at idle and 40lb under load even when this condition occurs.  I started to work on putting plugs, wires, cap and rotor last night but did not finish.  The plugs on the driver side seem to have more wear (very black) than the passenger side.  Does anyone have an opinion as to whether I''m on the right track or may I  be dealing with a more serious condition? Any help or advice would be appreciated - I just want to drive my new vette!
thank you

  
scooterman -> RE: 1991 Vette surging/misfire loss of power (7/1/2008 6:20:16 PM)

man this is deja vuE all over again!! Your symptoms are extremely similar to mine. mines an lt1 but I have to believe they are set up the same way. PLEASE let me know if you solve yours and I''ll certainly do the same
Richard

mech259 -> RE: 1991 Vette surging/misfire loss of power (7/1/2008 7:02:46 PM)

Change your fuel filter, 1st. I''m assuming there are no CE light or codes.

myfirstone -> RE: 1991 Vette surging/misfire loss of power (7/2/2008 7:31:03 AM)

Thanks for the advice.  All though the pressure is checking ok, the filter was on the to do list anyway.  I guess just because pressure is ok that doesn''t mean the volume is adequate.  I will complete the tune up and try the filter and see where I am at.
thanks

myfirstone -> RE: 1991 Vette surging/misfire loss of power (7/2/2008 7:36:23 AM)

i''m sorry, to answer your question there were no lights or codes related to this condition.
there were two codes before I drove the vehicle home from out of state.  I checked at a friends shop (out of state) and then cleared.
34 "open in ign 1 feed to deployment loop"
33 "steering diodeshort in arming sensor"

i was told that these have nothing to do with driveability issues, that they are related to the airbag system.

scooterman -> RE: 1991 Vette surging/misfire loss of power (7/7/2008 5:00:47 PM)

OK- TRY THIS! Unplug the vaccum to the egr valve and drive it. It may be opening up too quick. I did that to mine and I think it fixed it. It may turn the light on, but you can always clear the code if it does. Mine''s a 94 and so far no light. Anyway I''m going to leave it unplugged for a couple of days and if stays "fixed" I am going to replace it and clean all the ports
Richard

myfirstone -> RE: 1991 Vette surging/misfire loss of power (7/8/2008 9:34:33 AM)

Mech259 and Scooterman,
Thank you both for your advice.  After completeing a general tune up and replacing the fuel filter I discovered that the previous owner replaced quite a few trivial things eventhough basic maintence items have obviously been neglected for some time.  This led me to believe he knew of this problem and was throwing some parts at it trying to coreect it.  Upon further investigating by my regular mechanic the fuel pressure was not as good as I previously thought.  It behaved quite differently after letting the car idle for one hour plus.  To make a long story short the fuel pump and injector for the #4 cylinder were causing my problems.  He wrapped that up today and the vehicle passed PA emissions test so I should be good to go, at least for today! 

  

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